Mobile Engineer (React Native/Expo)

About the role

Onyx is building a consumer‑first trading platform that combines prediction markets, sports, crypto and real‑world events. We are looking for a Mobile Engineer with strong production experience in React Native, Expo and TypeScript to own and scale our iOS and Android applications.

Key responsibilities

• Design, develop and maintain high‑quality mobile apps using React Native, Expo and TypeScript.
• Own features from technical design through development, testing, deployment and monitoring.
• Manage builds, releases and over‑the‑air updates with Expo Application Services (EAS).
• Handle Apple App Store and Google Play Store submissions, including certificates, provisioning profiles and versioning.
• Integrate the mobile app with backend APIs and AWS‑based services.
• Build real‑time experiences powered by live data, WebSockets and streaming updates.
• Optimize performance, responsiveness, reliability and scalability.
• Create reusable components and contribute to a scalable mobile architecture.
• Collaborate with Product, Design, Backend Engineering and Infrastructure teams.
• Debug production issues and improve the overall customer experience.

Required profile

• 2+ years of professional mobile engineering experience.
• Strong production experience with React Native, Expo and TypeScript (Expo experience is non‑negotiable).
• Hands‑on experience shipping consumer applications through both the Apple App Store and Google Play Store.
• Deep knowledge of the end‑to‑end submission and release process, including app signing, provisioning and versioning.
• Experience with EAS Build, EAS Submit and Expo Updates.
• Solid understanding of mobile architecture, state management, testing, debugging and performance optimization.
• Experience integrating mobile apps with REST APIs; AWS experience is a plus.
• Product intuition, attention to detail and a focus on polished consumer experiences.
• Comfortable owning mobile features and releases end‑to‑end in a fast‑moving startup environment.

Required skills

• React Native
• Expo
• TypeScript
• iOS
• Android
• Apple App Store
• Google Play Store
• EAS Build
• EAS Submit
• Expo Updates
• Mobile architecture
• State management
• Testing
• Debugging
• Performance optimization
• REST APIs
• AWS (preferred)
• Swift (optional)
• Kotlin (optional)
• WebSockets
• Animations